TEXT-BOOK OF BACTERIOLOGY. 5 



threads, then again as larger or smaller rods, or even as clearly 

 circular cells, and lastly also as spiral-shaped bodies. This species 

 has been thought by some to belong to the bacteria, and has been 

 cited to defend the views regarding the apparent changes of form 

 already mentioned. 



Now, the above-named organisms most certainly do not belong 

 to the bacteria, although they may be very closely allied to them. 



There are genuine bacteria which possess chlorophyl (leaf-green), 

 and which therefore present, when they gather without distinction, 

 all the colorless forms of vegetable life. Crenothrix, cladothrix, 

 and beggiatoa are distinguished by an indubitable point-growth ; 

 that is, they strive to prolong themselves bj' progressive lengthen- 

 ing, and shoot from a narrow beginning into a point, which widens 

 out more and more — a proceeding of which we find no indication 

 whatever among the bacteria. Add to this the peculiar branching 

 of cladothrix, and lastly the pleomorphism, and we have convinc- 

 ing proofs of the ditference between these organisms and the bac- 

 teria proper. 



We may therefore maintain that, thus far at least, a many- 

 formed species of bacteria has not been observed, and the rule, 

 " One can distinguish by the growth and form clearly recognizable 

 genera and species of bacteria, which do not run into each other, " 

 remains as the general result of our investigations on this question. 

 The question of classification might be discussed indefinitely, but 

 of what consequence is it ? The bacteria interest medical men prin- 

 cipallj' from an etiological standpoint, because in them we find the 

 exciters of a number of virulent diseases. All the rest, the nomen- 

 clature and purely theoretical study, we may safely leave to the 

 proper persons, the botanists, in whose hunting-ground we have 

 already ventured far enough. What we know of the bacteria in 

 general, in a word is as follows : The bacteria are the lowest mem- 

 bers of the vegetable kingdom, closely related to the lower algae. 

 They di\ade themselves in a series of species, well defined by growth 

 and form, which do not run into each other. Of the forms in which 

 the bacteria appear we know the globular bacteria, or micrococci ; 

 the rod-shaped bacteria, or bacilli; and the screw-like bacteria, or 

 spirilla. 



II. STRUCTURE— FORMATION OF GROUPS— FLAGELLA. 



I have already mentioned that we must regard the bacteria as 

 cells, for they grow and divide and form fruit as such. 



The strongest argument in favor of their cellular nature is the 

 fact that they possess a central mass composed of albumin, or pro- 



